Mosaic plans to develop a novel transrectal gamma probe that will detect and localize prostate carcinoma in and around the prostate. The system has been optimized for detecting and localizing ProstaScint uptake sites in and near the Prostate. The probe is a miniaturized, collimated solid-state detector. The design is constrained by the requirements that the probe be small enough for intra-rectal use and that it operate effectively for the 247 keV emission of 111 In-labeled ProstaScint. The Phase 1 program describes and will experimentally evaluate two complementary collimation schemes for the probe. One is a conventional, but low-sensitivity multi-hole collimator. The other is a novel, high-sensitivity collimator. The Phase 1 plan consists of three parts: 1) constructing the collimator evaluation platform (phantoms, fixtures, acquisition hardware, processing software) required to carry out the experiments, 2) carrying out a set of proof-of-principle experiments designed to establish the feasibility of using one or both collimator designs a miniaturized probe to intra-rectally detect and localize prostate cancer, and 3) summarizing the results and conclusions of Phase 1 and laying the foundation for the Phase 2 Clinical Prototype. PROPOSED COMMERCIAL APPLICATIONS: Mosaic's gamma probe would aid Urologists working with Nuc Med Physician or Radiologist to verify prostate cancer and help direct biopsies toward the cancer. The probe could detect and localize the cancer within area of the prostate to be sampled rather than the current practice of performing multi-needle sampling or additional biopsies. It would be used after an elevated PSA has been confirmed but before biopsy.